fix: open each post as its own window from the Posts window

[epeicher]

Summary

Clicking a second post in the Posts window refocused the first post's window instead of opening a new one.

deriveWindowId() collapsed every post.php?post=X&action=edit URL to the same ID (post-php) because post wasn't in IDENTITY_PARAMS — only post_type, page, taxonomy, and path were significant. So every post-edit URL produced the same window ID, and windowManager.open() saw a matching window and refocused it.

Fix

Add post to IDENTITY_PARAMS so post.php?post=123&action=edit → post-php-post-123 and post.php?post=456&action=edit → post-php-post-456. Every code path that derives a window ID (Posts-window row click via openAdminUrl, in-shell <a href> clicks via the link interceptor, dock-icon clicks, session restore, geometry lookups) benefits automatically since they all funnel through deriveWindowId.

Test plan

• npm run lint, tsc --noEmit, full vitest (1116 tests) green
• New regression test in tests/vitest/utils.test.ts locks in distinct IDs for two post URLs
• Manual: open the Posts window, click Post A → opens Post A window; click Post B → opens Post B as a separate window; click Post A again → refocuses the existing Post A window

[github-actions]

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